1. Field of the Invention
The present invention relates to the field of heating, ventilating, and air conditioning (HVAC). More specifically, the present invention relates to a novel connector for connecting flex-duct to a fitting, such as a tee, an elbow, y-branch connector, starter collar or a register boot.
2. General Background and State of the Art
With the rising costs of energy and increased attention to environmental concerns, businesses, consumers, and governmental agencies at all levels are bringing concerted efforts to reduce energy consumption and waste and to protect the environment. In the HVAC trade, several major changes have been made in recent years to address these concerns, such as the use of less harmful refrigerants, the development of more energy efficient equipment, more stringent energy and environmental codes, and enforcement of those codes.
One area in the HVAC trade that has not been effectively addressed and that has been identified as a leading source of energy loss in both domestic and commercial applications is air leakage due to connection failure in flex-ducting. Flex-ducting is a remarkable product and is the most commonly used form of residential air ducting, because of the ease with which it may be routed through and around, over and under rafters, electrical wiring and fixtures. It has effectively eliminated the limitations of a rigid sheet metal duct system. Flex-ducting is available in many diameters, generally ranging between four inches and 22 inches, and is usually sold in 25-foot lengths that can be easily cut to an appropriate length. Flex-ducting is constructed in three layers: 1) an inner liner having a wire coil support; 2) an insulation layer over the liner; and 3) an outer jacket covering the liner and the insulation layer. Flex-ducting typically is run between sheet metal plenum starter collars to other sheet metal fittings such as Y's, elbows, T's and register boots. While, as mentioned, flex-ducting is easy to cut to length, connecting the flex-ducting ends to a fitting is where the potentially serious problems lie and also represents the most time-consuming and labor intensive part of the installation of flex-ducting.
The conventional method used by HVAC installers to connect flex-ducting to a fitting has been to first fold back the outer jacket and insulation from the liner, slide the liner onto the fitting, and wrap duct tape around the connection at least three times. Most applicable codes specify the type of duct tape and the number of times the duct tape must be wrapped around the connection between the liner and the fitting; three times around a duct edge and a fitting is a typical code requirement. After that part of the connection process is complete, the insulation and outer jacket are pulled over the duct-taped connection and another type of duct tape (as specified in most applicable codes) is wrapped around the connection between the insulation/jacket and the fitting a specified number of times. After that step is completed, a securing means such as a zip tie is usually secured around the connection.
There are problems with the just-described method of connection that have led to considerable waste of energy due to leakage of air at the connection of the flex-ducting and the fitting. Installers frequently work in confined spaces and may not be able to readily view or comfortably reach the entire area of the connection, which can mean that the application of the duct tape is awkward and the quality of the connection is compromised. The biggest problem with this type of connection over time, however, is that the flex-ducting comes apart from the fitting and cause considerable leakage, either because of movement of the flex-ducting or because the duct tape becomes brittle from heat or age. Plastic zip ties become brittle and break over time.
While most such connections may hold well enough to pass an initial inspection, the continuous flow of hot or cool air will eventually dry out the duct tape and the connection will fail. Other contributing factors that lead to connection failures are dust cleaning, movement of other trades people moving around, over and under the flex-ducting, or movement of the flex-ducting by such individuals during other projects.
During 2004, the United States government, along with the State of California and several Energy Commissions funded a study of durability of various duct tapes and adhesives used for connecting flex-ducting to fittings. The conclusions of the study were two-fold: 1) none of the duct tapes or adhesives proved durable enough to pass the tests of time and temperature; and 2) due to features inherent in the design of flex-ducting, the insulation and outer jacket cover or wrap the connection between the liner and the fitting from view, thus impeding enforcement of the use of approved sealants, duct tapes, or procedures. No solutions were offered.
During 2007, the State of California Energy Commission tried to address some of the problems inherent in the use of flex-ducting with the passage of code amendments and requirements under Title 24. Under the amended and updated codes, duct leak tests are required during installation. While this requirement may lead to more diligent and careful installation practices, it can only increase the time and costs of installation and does nothing to improve the flawed connection procedure or increase the longevity of the inferior materials used in the currently mandated method of flex-duct connecting. Flex-duct connections will continue to fail with time and the failures may occur in hard-to-access locations.
It would therefore be desirable to provide a flex-duct connector and method of connecting flex-ducting to fittings that overcomes the disadvantages of the conventional connection and installation methods.